The electric current leakage path of thin-film transistors (TFTs) mainly includes liquid crystal capacitor leakage and TFT leakage. The former is that current is leaked from a pixel electrode to a common electrode, and the latter is that current is leaked from a pixel electrode to a data line. Thus, the leakage of the latter is related to the voltage on the data line. In a leakage current conduction mechanism of a TFT device, hole current mainly formed by channel thermionic emission, for instance, leakage current of amorphous silicon (a-Si) products, will greatly increase under the condition of illumination.
Indium gallium zinc oxide (IGZO) is a new material for preparing active layers of TFTs. Firstly, IGZO transistors have smaller size, so that the device can be thinner. Secondly, IGZO transistors are fully transparent and not sensitive to visible light and hence can greatly increase the aperture ratio of components, improve the brightness and reduce the power consumption. In addition, in the aspect of electron mobility, the mobility of IGZO carriers is 5 to 10 times of that of a-Si. The threshold voltage shift is almost consistent and improved by 20 to 50 times compared with a-Si materials. Thus, the on-state current characteristic is good and the progress is very remarkable. Moreover, IGZO panels have an overall improvement in main performance parameters of panels compared with a-Si TFT panels.
In order to reduce the optical contact area of oxide active layers (e.g., IGZO active layers) and reduce the light-induced leakage current, oxide TFTs generally adopts light shield structures. As illustrated in FIGS. 1 and 2, a gate line 102 is disposed below an oxide active layer 104, a source electrode 106 and a drain electrode 107, so that the gate line 102 can shield the oxide active layer 104 formed in the channel between the source electrode 106 and the drain electrode 107, and hence the possibility of the production of electron-hole pairs in the case of illumination can be effectively reduced. Thus, the leakage current (off-state current) is less affected by illumination.